I'm using Unfold3D 2018.0.45. The Box autoseams produce good UV on most of models like table, chair but fails on model like leaf, plants.
Please take a look at the below image, I compared the result of Unfold vs Flatiron (hard surface mode - which look like using Box method too). Unfold packing is a lot better, but Flatiron does better unwrap on the leaf. I've attached these 3D models. I believe this is a bug cause I tried to set Sketch Control to 0.99 but still having the same result.
Hope this will be fix soon, great products Unfold3D !
Also, I think Reweld should have limit by maximum size of island (similar to area filter in Auto Select Islands), because sometimes it'll weld large islands like below, which makes UV packing unoptimize: